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The electromigration behavior of a solder joint with Cu-core/Sn-shell structure under 1.3×104 A/cm2 was investigated in this work. As Cu has lower electrical resistivity than Sn, the Cu core was chosen primarily as the path for current flux. Compared with the traditional solder joint, this core/shell solder has two couples of cathode and anode due to the additional Cu core. It is found that most morphology...
White tin (or β-Sn) has a body-center tetragonal (BCT) crystal structure with lattice parameters of a = b = 5.83 Å and c = 3.18 Å. We found that the orientation of the β-Sn phase strongly correlated with the Ag content in the Sn-Ag-Cu solder joints. When the Ag content is equal to or greater than 3 wt.%, the Sn grains display a strong preferred orientation of the c-axes in the direction parallel with...
This paper focuses on the link between initial electrical resistance of Through Silicon Via (TSV), and possible failure occurring during Thermal Cycling Test (TCT) and electromigration (EM) tests. Physical analyses reveal the presence of a carbon impurity layer at bottom of the higher resistance TSVs. This impurity induces failure during TCT, but has no impact on EM time to failure distribution. We...
A demand for small form factor in IC packaging has lead to a reduced bump size and an increased current density. The high current density accompanying with Joule heat induces an electromigration failure. In this study, we investigated the effects of under bump metallization (UBM) on the electromigration failure. Three types of UBM such as Cu 5 μm, Cu 10 μm and Cu 5 μm/Ni 2μm were compared with 60...
Void formation, intermetallic compound dissolution and metallization consumption at cathode interface are major degradation processes of electromigration in solder joints, but decisive factors for the phenomena are not clear. The article provides a new perspective to describe the electromigration behavior. We analyzed the temperature effects on Cu and Sn electromigration fluxes in Sn. The calculated...
The line-type Cu/Sn/Ni interconnects were used to determine the effect of electromigration (EM) on the Cu-Ni cross-interaction under the current density of 1.0×104 A/cm2 at 150 °C for 100 h and 200 h. For the purpose of comparison, the line-type Cu/Sn/Ni interconnects were also aged at 150 °C for 100 h and 200 h. After soldering, Ni3Sn4 and Cu6Sn5 IMCs formed at the Sn/Ni and Sn/Cu interfaces, respectively...
The effect of electromigration (EM) on the solid state interfacial reactions in line-type Cu/Sn/ENIG interconnect was investigated under the current density of 5.0×103 A/cm2 at 150 °C for 100 h and 200 h. The Cu/Sn/ENIG specimens were also aged at the same temperature and durations for comparison. After soldering, Cu6Sn5 and Ni3Sn4 IMCs formed at the Cu/Sn and ENIG/Sn interfaces, respectively. During...
The combined effects of thermomigration (TM) and electromigration (EM) were investigated in Cu/Sn3.0Ag0.5Cu/Ni solder joints by applying a 5×103A/cm2 DC current to the joints. With a thermal gradient, the Cu atoms and Ni atoms were found to migrate towards the lower temperature side while the Sn atoms were found to migrate towards the higher temperature side. For the solder joint stressed with a 5×10...
The relationship between electromigration behavior and the crystallographic orientation of Sn grains was investigated. The test vehicle was the Cu/Sn-3.0wt%Ag-0.5wt%Cu/Cu dummy flip-chip model, and the applied current density was 15 kA/cm2 at 160°C. The depletion of Cu atoms at the cathode side is a major cause of the early circuit failure. Electromigration behavior and the growth of intermetallic...
We report an experimental investigation into the controlled fabrication of metallic nanospheres on the tip of nanotubes. The fabrication process, nanobubbling, is based on nanofluidic mass delivery at the attogram scale using metal-filled carbon nanotubes (CNTs). Two methods have been investigated including electron-beam-induced bubbling (EBIB) and electromigration-based bubbling (EMBB). Under the...
The intermetallic compound (IMC) growths of Cu pillar bump with shallow solder (thin Sn thickness) were investigated during annealing or current stressing condition. After reflow, only Cu6Sn5 was observed, but Cu3Sn formed and grew at Cu pillar/Cu6Sn5 interface with increasing annealing and current stressing time. The kinetics of IMC growth changed when all Sn in Cu pillar bump was exhausted. The...
A trade-off property of CuSiN between EM improvement and line resistance increase was resolved by a breakthrough that leaves oxygen at grain boundary of Cu line surface before CuSiN formation. Then, the combination of CuSiN and Ti-rich TiN (Ti(N)) barrier metal (-BM) was applied. Oxygen left by weakening process strength of CuOx reduction lowered line resistance, because Si diffusion causing line...
A Ti/TaN multi-layer can achieve a highly reliable Cu interconnect with a porous SiOC (ELK; k <; 2.5) structure. Ti shows good wettability with Cu and unique properties with extreme low-k (ELK)-structured interconnects. On the other hand, Ta is known to be an effective barrier to Cu diffusion. We confirmed that the Ti barrier is different from the Ta barrier from the viewpoint of metal-oxide behavior...
Electrical voltage polarity-dependent failures of Ti/TiN/W via fuses were observed and analyzed by microstructural analyses and flux calculations based on the simulated Thomson-shifted temperature profiles. In the forward program, electromigration (EM) was in the same direction as thermomigration (TM), while in the reverse program, EM was in the opposite direction from TM, which made the forward program...
We observed various EM-induced failures in current-stressed Cu/Sn/Cu flip-chip solder joints. EM-induced Cu-pad consumption occurred at the current-entry point (maximum current-density) on the cathode interface, and voiding occurred at the other joint corner away from the current-entry point (minimum current-density). We believe that the above various EM-induced failure modes were the result of different...
The requirement for smaller devices but with much greater performance leads to a boost in current density and damage caused by electromigration. Recently, some researches show that the grain orientation changes during current stressing. In this study, the solder of SnAg2.6 with 2 um-thick UBM layer of Ni and 20 um-thick copper pad is used. Electron Backscattered Diffraction (EBSD) is applied to investigate...
The effect of electromigration on the solid state interfacial reaction of pure Sn and Cu was investigated. Two electron current densities (1.0times104A/cm2 and 5.0times103A/cm2) were applied to line-type Cu/Sn/Cu interconnect at 150degC. The same types of intermetallic compound (IMC), Cu6Sn5 and Cu3Sn, formed at the Sn/Cu interfaces independent of electric current. A high current density caused a...
Sn whisker growth is considered as a crucial reliability issue in the electronic packaging industry, especially with the massive application of Pb-free solder alloys. In this paper, we report our fundamental studies on Sn whisker growth through accelerated tests. Excessive rare earth element addition is one way we employed to investigate the kinetics of whisker growth. Several aspects of the morphological...
Electromigration (EM) of micro bumps of 50 mum pitch was studied using four-point Kelvin structure. Two kinds of bumps, i. e., SnAg solder bump and Cu post with SnAg solder were tested. These bumps with thick Cu under bump metallization (UBM) were bonded with electroless Ni/Au (ENIG) pads. The results showed different EM features comparing with larger flip chip joints. Under various test temperatures...
For the past several years, the semiconductor industry has been responding to the RoHS directive to eliminate certain hazardous substances from electronic components. One of the areas where work is still ongoing to comply is in the area of flip chip interconnects. Currently, leaded flip chip interconnects are allowed under an exemption in the RoHS directive due to a perceived lack of a technically...
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